CHAPTER III 

 MECHANISM OF METABOLISM 



General Theory oe Metabolism 



Anabolism, Katabolism, Metabolism. — In the introduction to the 

 Physiology of Microorganisms, it was stated that microorganisms need 

 food for at least two different purposes: building material and building 

 energy. They may need it for other purposes also, e.g., for motion. 

 The sum of all changes which the food undergoes in the body, including 

 the deterioration of the cells, is called metabolism. Metabolism con- 

 sists of several separate functions: One of them is the construction 

 of new cells, or parts of cells, called anabolism, another the deteriora- 

 tion of cells, called katabolism, and the most important quantitatively 

 is the fermentation or respiration. The fermentation or respiration 

 processes are fairly well understood; many of them can be produced 

 in the chemical laboratory without microorganisms. Katabolism is 

 the sum of many processes some of which are well understood while 

 others are still unknown. The synthetic, anabohc processes of the 

 cell, however, are almost entirely unknown, and we can only speculate 

 regarding the various means by which the cell grows. The explana- 

 tions of the different cell activities began, as in most other fields of 

 theoretical bacteriology, with a close, analogy with animal and plant 

 metabolism, but owing to the comparative simpUcity of the micro- 

 organisms, they led to the establishment of new facts and theories which 

 proved afterward useful for the understanding of the metabolism of 

 the more complex organisms where the multiplicity of facts prevented a 

 clearer insight into the separate processes. 



Intra- and Extra-cellular Fermentation 



Decomposition of Insoluble Food. — It has been stated before 

 that many microorganisms feed upon cellulose, starch, fat, gelatin, 

 keratin and other insoluble compounds. It has also been previously 

 stated that microorganisms, with the exception of some protozoa, 



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